Numerous types of openable current-measuring devices are known. The commonest type is a current-measuring clamp which is put into position to measure the current flowing in a cable at a given moment and is then removed after the measurement has been performed. When the current flowing along a conductor is to be measured on a permanent or on a semi-permanent basis, it is generally not desirable to use a current-measuring clamp. The opening magnetic circuit of such a clamp is generally closed by a resilient member such as a spring, and under conditions of continuous use the clamp runs the risk of opening under the effect of the vibrations to which is it subject. Further, a current-measuring clamp is generally fitted with handles whose bulk is incompatible with the requirements of complex electrical installations.
When a current transformer is to be installed on a permanent or a semi-permanent basis, it generally comprises a magnetic circuit comprising two portions which are hinged to each other like a clamp and which are held clamped against each other by a bolt which extends perpendicularly to the end faces of the magnetic circuit portions. Such devices are difficult to manipulate because of the large amount of room that they occupy when in the open position. Further, it is generally difficult to control the clamping force applied by the bolts and the bearing surfaces may become distorted, thereby disturbing the transmission of magnetic flux through the gaps between the portions of the magnetic circuit.
Preferred embodiments of the present invention provide a current measuring device which is simple in structure, which is easy to put into place, and which provides good transmission for magnetic flux.